The invention relates to a key input apparatus capable of detecting input signals due to the actuation of a single key or the simultaneous actuation of a plurality of keys.
Generally, the key input apparatus is provided with a plurality of input operation keys and applied to various electronic apparatuses such as electronic computers and electronic musical instruments. A key matrix is devised in order to reduce the number of terminals of an integrated circuit of the key input apparatus when input signals produced by the key actuations are inputted to the electronic apparatuses. In this matrix construction, when a plurality of keys are simultaneously actuated, the called branching-out currents flow into current paths among the actuated keys, resulting frequently in erroneous operation. It is for this reason that diodes are provided at the cross points of the matrix which provide current branch paths. The provision of the diodes are defective in that, when the number of the keys is large as in the case of the musical instruments, the mounting work of diodes is troublesome and the reliability of the apparatus is deteriorated.